THE detection and identification of pterins in small quantities was carried out by Schopf and Becker1 in the course of their classical work on this class of pigments. They employed a chromatographic technique using 0·004 N aqueous hydrochloric acid or 0·01 N methyl alcoholic hydrochloric acid solutions on micro-absorption columns of alumina or frankonite. The technique of paper chromatography has now been applied successfully to certain of the common pterins, and as a result a method has been elaborated for the rapid identification of very small quantities of these compounds such as may be obtained by extraction of individual butterfly wings. Indications that this method might be applied in the pterin series had been given by Crammer2, who mentioned that xanthopterin and leucopterin could be concentrated by a paper chromatographic technique.